what does ‘the universe is flat’ mean? How can it be flat when there are stars, planets, galaxies etc. everywhere we look?

Question

what does ‘the universe is flat’ mean? How can it be flat when there are stars, planets, galaxies etc. everywhere we look?

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Answer 1

Flat in this case does not meant flat as in 2 dimensional, it means space is not “curved.” In other words’ it obeys Euclidean geometry, which is the geometry we’re all familiar with where parallel lines never meet and the sum of the angles in a triangle is always 180 degrees. In curved geometry, parallel lines *will* meet and the sum of the angles in a triangle will not necessarily be 180 degrees.